1. Field of the Invention
The present invention relates to a heating resistor element, a manufacturing method for the same, a thermal head, and a printer.
2. Description of the Related Art
Conventionally, in a heating resistor element provided in a thermal head of a printer, in order to improve heating efficiency of a heating resistor and to reduce power consumption, a hollow portion is formed in a region opposed to the heating resistor, and the hollow portion is caused to function as a heat insulating layer having low heat conductivity, thereby controlling an amount of heat flowing from the heating resistor to an insulating substrate side (for example, see JP 2007-83532 A).
As a method of forming the hollow portion, there is employed a method of etching a silicon substrate, and forming a concave portion (having a depth of 1 μm or more and 100 μm or less) to bond thin plate glass (having a thickness of 10 to 100 μm) serving as a heat accumulating layer thereon through anodic bonding performed at a temperature of 700° C. or less. In this case, it is difficult to manufacture or handle the thin plate glass having a thickness of 100 μm or less, and thus thin plate glass having a thickness, which is relatively easily handled, is bonded to a surface of the silicon substrate, and then a surface of a side opposite to a bonded surface is chipped by etching or polishing to obtain a desired thickness size.
There can be formed a concave portion including an aperture of a size substantially equal to the heating resistor and having a large depth size by performing anisotropic etching, but the formed concave portion has a shape with a corner which is sharply bent. Accordingly, stress concentration is caused at the corner by heat or a load, which may generate a break or a crack therein. Besides, in this case, the thin plate glass which is bonded to the silicon substrate to block the aperture of the concave portion is also applied with a stress due to the stress concentration caused at the corner in the vicinity of the aperture of the concave portion of the silicon substrate, and hence thin plate glass having a thickness size of 10 μm or less cannot be used, which limits an improvement in heating efficiency.
On the other hand, in a case of performing isotropic etching, the concave portion is formed so that its corner has a curvature radius of a predetermined value or more. However, in this case, the depth size of the concave portion can be set to not more than about a half of an aperture size of the concave portion, and in a case of providing a deep concave portion, the aperture size becomes larger with respect to the heating resistor, which makes it difficult to obtain a desired strength.